Isotope separating apparatus control



Aug. 25, 1959 s. w. BARNES ISOTOPE SEPARATING APPARATUS CONTROL Filed Oct. 8, 1946 IN VEN TOR. fi'azzey wfiarzzes Unitcd States Patent C ISOTOPE SEPARATING APPARATUS CONTROL Sidney W. Barnes, Rochester, N.Y., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application October 8, 1946, Serial No. 701,906

6 Claims. (Cl. 250-419) This invention relates generally to isotope separating apparatus of the electromagnetic type, commonly referred to as a calutron, and is more particularly concerned with improvements in methods of and means for controlling the position and condition of the ion beam of such calutrons for optimum operation.

While the apparatus of the present invention is not limited to the separation of the isotopes of any one element, it must of necessity be specially adapted for the masses involved, and in order for its principles to be clearly understood, the invention will be described as embodied in apparatus adapted for the separation of the uranium isotopes having atomic weights 235 and 238, the isotope having an atomic weight of 234 being ignored.

In such calutrons, a beam of positive ions of uranium is formed and projected at a high uniform velocity into an evacuated region traversed by a substantially uniform magnetic field at right angles to the direction of motion of the ions. As a result, each particular ion is caused to describe a circular path having a radius proportional to the square root of its mass. In this way the original single ion beam is split into two more or less distinct component beams, one of which consists of uranium ions having a mass of 238 and the other of which consists of uranium ionshaving a mass of 235. Because of a geometrical focusing action, these two beams are most distinctly resolved after the completion of 180 of their circular path, and the U and U ions may be separately collected at a receiver located at this point.

I An important consideration in the optimum operation of such calutrons is the ion beam control or monitoring problem, which in turn may be divided into two separate problems. First, the ion beam as awhole must be positioned with respect to the receiver such that the U and U beams fall correctly into their respective receiver pockets. Secondly, the individual beams must be focused on sharpened to as great an extent as possible, that is, the resolution of the beams must be good at the receiver. The control to attain both these conditions must be effected continuously while the calutron is in operation.

One prior method of controlling the ion beam such as to provide optimum operation was first to adjust the variables controlling the position of the whole ion beam with respect to the receiver so as to provide a maximum reading on the meter connected to the U collecting pocket, and that having been done, to then adjust the variables controlling the focusing or resolution of the beams such that the ratio of the U meter reading to that of the U meter reading was a maximum.

The above-described method of control, and other prior methods, however, are all particularly adapted to the case where the U ion beam is small compared to the U ion beam, that is, where the relative proportions of U and U atoms in the charge material are substantially the same as those occurring in nature. A different control problem is presented in the case where the charge material has already been enriched with respect to U atoms, and it has been found that prior methods By the present invention, the inventor has provided a simple, eflicient, and accurate control system for a calutron operating with uranium charge material which has been previously enriched with respect to U atoms. Thisvcontrol system is particularly applicable to the separation of two adjacent isotopes of any material wherein the relative proportions of the two isotopes are of the same order of magnitude. As a result of previous isotope enrichment processes, any two adjacent isotopes of any material may have arrived at a state of substantially equal relative proportions, as described above'with respect to the U and U isotopes. Also, certain adjacent isotopes of certain materials occur naturally in substantially equal relative proportions. Examples of such isotopes are: Mg (11.5%) and Mg (11.1%); Ti (7.95%) and Ti. (7.75%); Ti (5.51%) and Ti (5.34%); Kr (11.53%) and Kr (11.53%); M0 (16.3%) and M0 Pdlos and Pdlgg Agloq and Ag og Cdno and Cdnl (13.0%); Su (5.5%) and 811 (6.8%);Sb (56%) and Sb (44%); 8m (17% Sm (14%) and 8111 B11151 and B11153 Dy sg (24.6%) and Dy (24.6%); w 30.1%) and W 0313 and 03137 and Pdzog (23.59%) and Pd207 (22.64%).

In accordance with the principles of the present invention, the calutron receiver or collector is provided with an additional insulated electrode positioned intermediate the usual U collecting pocket and the U collecting pocket. As will later be described in detail, the deionizing current which flows from ground to this additional electrode is a minimum when the ion beams are properly positioned and focused. The method of control, then, comprises the steps of adjusting the vari ables controlling the position of the beams with respect to the receiver, and also the variables cont-rolling the focus of the beams, so as to minimize this deionizing current to the additional electrode.

Accordingly, it is the primary object of the present invention to provide a method of and means for controlling a calutron ion beam for optimum operation.

Another object of the invention is to provide a novel calutron receiver particularly adapted to provide an ion beam current indication useful in determining the attainment of optimum operating conditions for the calutron.

Still another object of the invention is to provide a novel calutron receiver having, in addition to the usual insulated pockets for collecting the component isotope ion beams, an electrically independent electrode intermediate said pockets.

A further object of the invention is to provide a novel calutron receiver having, in addition to the usual insulated pockets for collecting two individual isotope ion beams, an insulated electrode positioned to receive the inner adjacent fringes of said beams.

Still a further object of the invention is'to provide a method of ion beam control wherein the variables controlling the position of the ion beam are first adjusted until a minimum ion current is received at a region intermediate the component isotope ion beam collecting pockets, and then the variables controlling the focus of the ion beam are adjusted until a new minimum ion current is received at this region.

Another object of the invention is to provide a method of ion beam control wherein the ion current received at a region intermediate the individual isotope ion beam collecting pockets is minimized by suitably controlling the position and focus of the beam.

Other objects and advantages will become apparent from the specification taken in connection with the acits additional ;electrode.

companying drawings wherein one embodiment of the invention is-illustrated.

In the drawings, Fig. lis a diagrammatic sectional view of a calutron showingthe new type receiver with *Fig 2 and Fig. 3 'illustrate -typical l beam intensity patterns-for the' U and U beams across theyface of the receiver useful -in ei'cplaining the princip-les of the invention.

.Referring now to Fig. 1, reference numeral 1 re resents an evacuated vessel or tank .which itwillbe understood -is'-transversed by a substantially uniform 'magneticfield at right angles to the paper and produced by an electromagnet, one pole--piece 2 of which is shown. The magnetizing winding 3 of-th1s-magnet is supplied with magnetizing current from a power -and control panel 4. -It will-be understood that suitable apparatus isincluded in the control panel-4 for regulatinga-nd adjusting the magnetizing current flowing through winding 3.

Reference-numeral 5 1ndicates asource ofipositive :uranium ionswhich maybe of a type more completely described in US. patent application Ser. No. 561,271, entitled Temperature Control andrfiled October 31,

1944, in the name of Emmett V. Martin, nowPatent uranium compound contained therein. The uranium vapor is then channeled through "a passagewaytothe elongated constricted top portion of the ion source 5 which portion forms an ionization. chamber 6.

A slot'7 is formed in oneend of the ionization. chamher 6 and adjacent to this slotand. aligned-Jherewith is a filament, 8. FilamentAS is connected to afi-lament supply voltage-V3 at the power and contrdlpanel 4.

-One side of filamenLS is maintained at aQnegativepo- ''tional to the square root of themass of thatparticular tential V4 with respect to the source uuit5 sothat the source unit becomes an anode.forzthefilament. .As. a

result an electric arc.ismaintainedfromthe filament "8 through the slot 7 and lengthwise alongthe .interior of the ionization chamber-.6. .This are. serves .to disassociate and ionize the uranium compound vapor in. the

ionization chamber 6, and the resulting uraniumv ions are then withdrawn by an accelerating system through an elongated slot, not shown, in the top of-the-i onization chamber 6.

-The voltage supply V4, which-wi]l henceforth be re ferred to as the ionization-narc voltage, isone variable which controls the focusing of th e'ion'beams. This ionization arc voltage is always. maintained sufiic iently high so that the filament- 8v operates at maximum emission. Accordingly, by varying-the filament supply voltage V3, the ionization arc current which is another factor influencing the beam focus,v may be controlled.

Theacceleratingsystem comprises a slotted electrode 99- maintained at a high negative potential Vz with respect ro-the ion source-5, and a second slotted electrode--10 maintained at a high negative potential'vl with respect to the accelerating electrode 9. In operation the positive uranium ions in the ionization chamber fi are first acceleratedv by electrode 10, and t hen-fldecelerated some- 9 with respect toithe source units, this, potential V2 ,will bereferred to as: the. accelerating; potential, and the. electrode, 9 will be referred to as ,the. accelerating electrode. ,isince the potential V1 ortheaecnode'io l with respect tOuElSClIfOdE 9 does not inany way etfect the final velocity of the ions,,but rather primarily effects,

the resolution orfocusin'g of .theresulting.beams,.this

potential .Vl will'be referredto as. the .tocusing poten- 4 tial and the electrode 10 will be referred to as the focusing electrode.

All of the voltage supplies V1, V2, V3, and V4 may be, and preferably are, regulated and adjustable at the power and control panel 4. Although the ground con nection may be placed at any point in the potential sys tem, it is found to be more convenient in most cases to connectthe accelerating electrode 9 and the receiver 11 to ground, as shown. The polarities of the voltages are from.minus to plus in the direction of the arrows.

It will be apparent from theforegoing that the position of the ion beams with respect to the receiver may be varied by adjusting the accelerating potential V2, or by adjusting the magnetizing current which flows through the magnetizing winding 3. The shape of the beam intensity patterns, that is, the focusing of the ion beams, may be controlled by suitable adjustments of the focusing potential V1, the ionization arc potenital V4,

and the ionization arc current, which latter is controlled -vary the emission of the filament 8.

by varying the.filament supply voltage V3 to thereby Ashas been previously stated, the single ion beam emerging from theaccelerating electrode .9 is constrained to flow in a, circular path, and, since the radius of the circularpath taken by any individual ion ispropo-rion, two. more or less distinct ion. beamsareformed,

the. one ofsmaller radius (U beam) consisting of U ions, and the other of a larger radius (U beam) .consisting .of. U ions.

The receiver.11 comprises two insulated pocketsll and.13 for receivingthe U and U beams, respectively. An additional insulated electrode 14 is positioned intermediate the entrance slot cd to the U pocket 12 and the entrance slot ab to the U pocket -13 so as to receive that portion of the whole ion beam which arrives at the receiver in the region bc. Entrance slot cd to the U pocket 12 as'defined by face plate'16 andthe inner end of electrode 14, whereas entrance slot a b tothe U pocket 13 is defined by the outer end of electrode 14 and a second face plate .15. Pockets 12 and 13 and electrode 14 are connected to ground through ammeters 16, 17 and 18, respectively, which ammeters thereby provide a visual indication of the respective deionizing currents to the operator at the power 5 and control panel 4.

The detailed design of the receiver, which forms no part of the'present invention may be in accordance with conventional practice. Pockets .12 and'1 3 and electrode 14 are suitably supported in .thereceiver and arefinsulated from each other, and are preferably made of carbon to impart durability. Although in the drawings, it isindicated that the electrode 14 is supported at the ends, this electrodecould bemade integral withtheouter wall of, pocketv 1Q as a conducting insulated tip thereof.

Referring now, to Fig. 2, wherein a typical ion beam intensity patternis shown infits ,desiredpositionwith .respect to the. receiver, the U component pattern, and

the U component pattern. are indicated separately in 'solid lines. The total beam, intensity pattern U which is,..of. course, the sum of the separate U and U eomponents, is identicalwith the individual patterns .over .theregion .wherethesedo not overlap, and is indicated as a idotted. line in the .regionwhere overlapping occurs. i I

Since the U and U patterns are equail, in -FigpZ,

1 this figure represents the case where enriehedcharge ma- ,,terial,,containing equal numbers of U andU atoms .is -used.

.Inthis ,case. it is usuallyfdesirable to have the maximum or peak of the component beamintensity patterns positioned over the center of'the entrance slots to their respective. collector pockets, as-shownf It will be apparent that when this condition is attained the number of ions at the .receiver in the region b-c, which is the integral under the wave U from b to 0, will be a minimum. Moreover, if the focus of the beam is improved as much as possible so that the component patterns are made very sharp and very narrow, the current to electrode 14 is further minimized.

v In operation, the accelerating voltage V2 is first adjusted until the ion beam assumes its desired position with respect to receiver 11, the attainment of this condition being evidenced to the operator by a minimum reading on the ammeter 18 which records the deionizing current to electrode 14. This adjustment of the position of the beam with respect to the receiver could as well be accomplished, but rather less conveniently, by suitably varying the magnetizing current of winding 3 and thereby the intensity of the magnetic field. The correct positioning of the beam having been accomplished, the various factors which control the focus of the beam, namely, voltage supplies V1, V3, and V4, but notably the focusing potential V1, are then adjusted so as to sharpen the component beams to as great an extent as possible, the attainment of this condition being evidenced by a further minimizing of the reading of ammeter 18. After these initial adjustments have been made, it may be advantageous to repeat the entire procedure several times until the optimum operating condition is attained both with respect to the position of the beam and the focusing thereof.

In Fig. 3, a typical beam intensity pattern is illustrated for the case where the charge material employed contains perhaps twice as many U atoms as U atoms. In this case, it can be seen that the trough in the U pattern is no longer exactly centered between the peaks of the component patterns, but rather is shifted toward the pattern of the less abundant beam. Now when the beam is positioned so as to minimize the current to electrode 14 in accordance with the above-described operating procedure, the pattern will assume a position with respect to the receiver as indicated in Fig. 3. It will be noted that in this position the peaks of the component beams are no longer exactly centered over the entrance slots a-b and cd, but rather are shifted slightly in the direction of the U pocket.

This shift, however, is very slight and may even be desirable depending on the purpose of the particular run. If, for instance, the degree of enrichment rather than the quantity of material collected in the U pocket is the primary consideration, this shift will be advantageous. This is true because by offsetting the peak of the U pattern to the left from the center of the entrance slot ab, more U ions have been lost to pocket 12 than U ions, and although less actual material will be collected in the U pocket, nevertheless, the percentage of U therein will be greater.

On the other hand, if the most efficient collection of U and U ions in the pockets were the prime consideration, the shift would be undesirable. In such case, the amount of shift could be predetermined for the isotope ratio of the particular charge material to be used, and the shift could be avoided by a proper design of the receiver. As shown in the drawings, the entrance slots ab and c-d are indicated to be equal and the electrode 14 positioned exactly intermediate their centers. It will be apparent that for the isotope ratio represented in Fig. 3, it would be possible to design a receiver having entrance slot ab larger than ad, so that when the beam is positioned on the receiver so as to minimize the current to electrode 14 in accordance with the operating procedure outlined above, the peaks of the component beams would still fall at the center of their respective entrance slots. By proper design of the receiver 11 therefore, it is possible to compromise between clficiency of collection on one hand and enrichment of the material collected in the U pocket in any manner desired.

Since many changes in the above construction, and many apparently widely different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. The method of controlling a calutron ion beam for optimum collection of two adjacent component beams thereof at respective collecting pockets of a receiver, comprising the steps of adjusting the position of said beam with respect to said receiver until a minimum ion current is received at an electrode disposed in said receiver intermediate said pockets, and varying the focus of said beam until a further minimum ion current is received at said electrode.

2. The method of controlling a calutron ion beam for optimum collection of two adjacent component beams thereof at respective collecting pockets of a receiver, comprising the steps of adjusting the variables controlling the position of said beam with respect to said receiver until a minimum ion current is received at an electrode disposed in said receiver intermediate said pockets, and adjusting the variables controlling the focus of said beam until a further minimum ion current is received at said electrode.

3. The method of controlling a calutron ion beam for optimum collection of two adjacent component beams thereof at respective collecting pockets of a receiver, comprising the steps of adjusting the accelerating potential until a minimum ion current is received at an electrode disposed in said receiver intermediate said pockets, and adjusting the focusing potential until a further minimum ion current is received at said electrode.

4. The method of controlling a calutron ion beam for optimum collection of two adjacent component beams thereof at respective collecting pockets of a receiver, comprising the steps of adjusting the accelerating potential until a minimum ion current is received at an electrode disposed in said receiver intermediate said pockets, and adjusting the focusing potential, and the ionization are potential and current until a further minimum current is received at said electrode.

5. A calutron receiver comprising means forming a first insulated pocket disposed in said receiver for receiving and collecting a first ion beam composed of ions of a particular mass, means forming a second insulated pocket disposed adjacent to said first pocket for receiving and collecting a second adjacent ion beam composed of ions of a different mass, an insulated electrode disposed intermediate said pockets for receiving the inner adjacent fringes of both of said component ion beams, and meter means connected to said insulated electrode for indicating the deionizing current to said electrode.

6. A calutron receiver comprising means forming a first insulated pocket disposed in said receiver for receiving and collecting a first ion beam composed of ions of a particular mass, means forming a second insulated pocket disposed adjacent to said first pocket for receiving and collecting a second adjacent ion beam composed of ions of a different mass, an insulated electrode disposed intermediate said two pockets for receiving the inner adjacent fringes of both of said component ion beams, and respective meter means connected to said pocket forming means and said electrode, respectively, for indicating the respective deionizing currents to said pockets and said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,355,658 Lawlor Aug. 15, 1944 

